September 8, 2001 Meeting Notes
We got a huge amount accomplished today.
Phil and I drained about the last of the peroxide out of our
drum on Tuesday, but 2000 pounds of peroxide was supposed to ship out for us yesterday,
so we should have plenty in a couple weeks.
We will be getting 3000 pounds more some time later.
Loading ten liters into the lander took over twenty minutes
last time, between drawing the vacuum and loading it through the small
solenoid, and also caused the solenoid to overheat enough that it caused a
peroxide burp, so we took some major corrective action today. Our 3gpm, 30psi Teflon pump is supposed to
be here in a week and a half, but it was worth doing the changes just for the
next couple tests.
Russ brought a big AC powered vacuum pump to replace the
little battery operated ones we had been using. This draws a better vacuum, and drastically faster. A brought a bunch of 1/2" manual ball
valves that we could re-plumb the fill cart manifold with. We would up just putting one on the peroxide
loading side, because the nitrogen loads quick enough through the solenoid, and
the vacuum pump is probably the limitation on the suction side. I also got us a bunch of 1/2" ID clear
PVC tubing to load the peroxide with.
These changes brought the peroxide loading speed from 37 seconds a liter
(at best, for the first liter) to ten seconds a liter, a very welcome
Our new Fike burst discs and holders came in. These are really nice, and exactly what we
wanted a male pipe thread going directly to the burst disc holder, then
either an integral diffuser, or another pipe thread for a vent pipe. We got two 1/4" ones for the small
lander and test stand, and two 1/2" ones for the big lander, and
eventually our bigger test stand. We
had been using a relief valve on the big lander, and shuffling an NOS burst
disc with an adapter between the other tanks.
The new discs are all 1500 psi burst, which is half of what the NOS
discs are set for, so that gives us an additional safety margin.
We got all the pilot gear mounted on the big vehicle: an aircraft seat belt, the joystick, and the
twist throttle. We still need to do
some moving around and bracing, but everything is there and functioning.
I made a special version of our graphical flight simulator that
takes forwarded joystick and throttle data from the flight computer, so we were
able to stand on the pilot platform and fly the simulator on the laptop with
the real vehicle controls.
We got the electronics box mounted on the correct side, but
it is just hanging on by its mounting tabs, so we should probably get some
bracing all the way underneath it.
I have added two switches to the test stand electronics box
so we can open and close the ball valve with momentary toggle switches, instead
of the swap-the-alligator-clips-and-pulse-the-computer silliness we had to do
before. Both ball valves now have the
same CPC connector, and can be plugged either into the flight computer or the
test stand box.
Russ drilled the upstream vent hole into the ball
valve. We have been fine with the non-vented
ball for the test stand work, because the valve just opens and stays open until
the tank is blown down, but on the vehicle, the throttle will be opening and
closing, so we needed to make sure we never trapped a ball full of peroxide. It wouldnt likely be a problem sitting
there for a little while, but if it did start to catalyze for any reason, like
heat soak, the ball and valve would probably shatter like a grenade. All that you need to do to avoid this is
have a small hole drilled from the tank inlet side into the ball center
Phil finally found a supplier that would make us pure silver
foam without a multi-thousand dollar setup fee: Astromet is going to make us
enough foam for our four attitude engines for $512. If those work out well, we may get a larger batch for all our
future needs. Our current silver plated
nickel foam only seems to last for about a half dozen hops in the lander
attitude engines, so we hope to get something a lot more long lasting.
Phil also got us some pricing information for big filament wound
tubes from Beadle Plastic: 2 diameter
tube is about $40 per foot, plus shipping.
We are getting 20 of it, so we can experiment with two 10 long
airframes. We are also getting quotes
for the composite parts for the next-gen (supersonic) manned vehicle.
We changed two things for our first engine test: Russ made a new cavitating venturi with a
0.125 throat, and Phil cut additional catalyst discs to fill the area between
the inlet fitting and the spreading plate.
The area was pent-roofed, so he had to cut several progressively smaller
The first CV that we tried was a 0.26 throat, which we
believed to be too large to actually cavitate.
We wanted to have one small enough this time that it positively would be
the flow restriction.
The first test run sounded smooth for the first time ever on
this motor, but I screwed up and aborted the data logging before it got saved
out. We did another identical run (two
liters at 400 psi), and got the data properly.
It was perfectly smooth, and made 175 pounds, just about exactly the
jetting we want for the piloted lander central engine with a bit more pressure.
We had a smoothness that we were thrilled with, but we didnt
know if it was due to the CV or the extra catalyst, so we took the CV out and
let it run unrestricted for another two liter / 400 psi run. This run was also perfectly smooth, and made
400 pounds of thrust. The slight buzz
every other sample in the data is in the data collection hardware, not the
engine. There is a strange issue with
the RS232 voltage needs of the electronics, where if I have the laptop running
on battery it works fine, but if it is plugged into an AC line, it gets a buzz
in the A/D signal. I forgot to unhook
it for this test.
So, the cause of all of our rough runs was having a
moderately large open volume between the plumbing fitting and our spreading
plate. Problem solved. In the future, we will probably want to
design the motors to absolutely minimize that space, because adding catalyst up
there is probably limiting our maximum thrust by requiring some of the flow
past the spreading plate to be gaseous instead of all liquid, making that
likely the major flow limiter of the engine instead of the nozzle.
It is interesting to compare the thrust falloff vs blowdown
pressure between the two runs -- the unrestricted one falls off pretty much
directly with pressure, while the restricted one falls with the square root of
The big vehicle is set up exactly as if it was piloted
now. We ballasted it with a heavy punching
bag (donated by Christian Antkow) and a water jug so that it has the same
weight distribution as it will with a person on board. The total weight is now over 300 pounds dry,
with a significant chunk of it well off the centerline, so it would be a strong
test of the new attitude control software.
The water jug will add a bunch of sloshing to make things even more
The first test was with six liters of peroxide, pressurized
to 500 psi. This was our first test
with the large engine and ball valve, so I rolled the throttle on pretty
slow. It only got a few inches off the
ground before it used up all the peroxide.
For the second test, we loaded ten liters of peroxide and
increased the pressure to 600 psi.
It worked great! I
kept it very low to the ground, but the flight control software easily dealt
with the offset CG, and I could have put it anywhere I wanted. I am still sort of amazed that it seems to
be working as well in real life as it did in my simulations.
The pilots joystick is flopping all over the place while it
Ten liters of peroxide gives seven seconds of lift in this
configuration. We can load twenty
liters with the current tank, and we can get much longer tanks of the same
diameter if we want to do any long duration flights.
Russ took some pictures with his high-res digital camera today:
Big engine catalyst pack
Lander at the start of the day
Neil putting the big engine on the test stand
Phil and Neil putting the big engine on the tank manifold
John and Joseph working on the lander
Big engine and plumbing mounted to the lander
Anna jumping off the pilot platform
ToDo on Tuesday
New catalyst packs for small engines, because we could see
one of them just starting to stream a little bit on the last hop.
Some slightly larger engine jets for the big engine.
Put finishing epoxy over the big tank so we stop getting
carbon fiber itch.
Fix the manifold drips from the burst disc and the bottom
Make new seatbelt mounts three inches lower.
If all goes well, we fly a person next Saturday.